Oscillating water column (OWC) technology consists of a partially submerged structure with an underwater opening that enables the movement of the sea to create a compression and a vacuum of the air enclosed within the inner cavity or air chamber. When a wave acts upon the OWC device, it causes the water contained within the structure to move, thus pressing and pushing the air inside the chamber, making it pass through a turbine specially designed for this purpose. Once the water recedes, the air in the chamber is decompressed and suctioned through the turbine. A generator coupled to the turbine converts the rotational mechanical energy of the latter into electricity.
The turbines that are normally used in OWC devices are bidirectional, such as Wells, Setoguchi or bi-radial turbines, which are designed to rotate in the same direction regardless of the direction of the airflow. Thus, despite the alternating movement of the waves, the turbine and the associated electric generator can permanently spin at a high speed, since their spin direction is always the same.
There is a second approach based on the use of unidirectional turbines, that means these turbines only operate with a single air inlet direction, such that the airflow must be rectified. The airflow is rectified by means of a set of non-return valves. There are different designs for devices with this approach using different arrangements with more or fewer valves and turbines. Among the most documented of these are the following:                One turbine, four valves, circuit open to the atmosphere        One turbine, two valves, circuit open to the atmosphere        One turbine, two valves, circuit closed        
In this last case, the column at the turbine inlet is above atmospheric pressure, and the column at the outlet is below atmospheric pressure.
Given the natural oscillation of the waves, the horizontal cross-section of these columns cannot be very large, as the effects of the crest and trough of the wave would be combined in the same column, which would create an averaging effect whereby the variation in the mean height of the water column would be zero, and the energy thereof could not be exploited.
In order to enable an increase in the power of the devices and reduce operating and maintenance costs, while avoiding the aforementioned averaging effect, several columns may be joined together in a single platform, spaced far enough apart that they do not significantly diminish one another's waves, and moreover improving the stability of the overall energy output. In the case of bidirectional or unidirectional turbines with rectified airflow, the devices of the platform must be independent in terms of both the water column and the air chambers. This is due to the fact that, were they to be joined, the pneumatic pressure of one chamber would be cancelled out by the vacuum in the other.
One advantage to situating several devices in the same platform is that all of them share the equipment for converting the alternating current generated by each one of them into a continuous current in order to connect the energy from each one of them to a single cable and convert it again into alternating high-voltage energy to be transmitted, and which can be injected into the grid through an electrical substation. Moreover, the overall dimensions of this infrastructure are smaller than the sum of each one of them separately, since the power peaks of the various devices tend not to coincide in time.
In the specific case of closed-circuit unidirectional turbines, the pressure and vacuum chambers of each one of the devices may be joined together in order to feed a single, larger and more efficient turbine. In this case the difference in pressure and flow are also more stable, as with the power produced.
These constructions, which may be rather large floating structures, or may be situated on the shoreline or on breakwaters, include large tubes where the volume of water enters. The design of said constructions tends to vary in order to obtain higher energy efficiency, and they are more robust so as to withstand the force of the sea, are modular so as to reduce costs, and have unique designs for better maintenance.
Thus, the various known designs bring different technical solutions to the state of the art. Patent GB 2161544 presents a multi-column platform with a unidirectional turbine that operates on a closed circuit between two vacuum and pressure manifolds fed by the various chambers. The device is long enough so that at the same moment there may be columns compressing and expanding. Mechanical or water non-return valves are used to control the flow of the pressure created. There is a version that includes an extra pressure tank that may be fixed or have a variable volume.
Other patents present design advantages over the same setup. For example WO 2007057013 designs a setup facing towards the direction of the waves with a boomerang shape, anchored to land by its tip or by its ends. Likewise, the vacuum forces help to reduce loads on the platform by managing to reduce its weight, which opens up the possibility of distributing the multiple columns in two arms forming a V, and which allows for the depth in the water to be adjusted by means of air valves connected to the exterior.
Patent WO 2007131289 presents a generator that comprises a body made up of a plurality of chambers with non-return valves. A first vessel receives the air from a first set of chambers and passes it through the generator, which sends it into a second set of chambers that also have non-return valves.
All of the solutions using pressure and vacuum chambers are equipped with a turbine between these two closed volumes of a limited size, such that the volume to be sent through the turbine is smaller, and the flow more variable, thus directly reducing performance.
All of these solutions entail large oscillations in pneumatic power, leading to a reduction in the performance of the devices. It would therefore be desirable to develop a device for capturing wave energy that improves upon the features of the existing devices.
The new device, which is the subject matter of the invention presented herein, has two turbines arranged in direct contact with the atmosphere, one of them being connected to a pressure accumulator and the other to a vacuum accumulator. Said accumulators act as manifolds and dampers, without the need for connecting piping or any additional tanks. All of this enables the device to have improved performance due to the reduction in head loss and to more stable turbine operating conditions, as well as a reduction in the cost of the energy generated.